1. Technical Field
The present invention relates to data storage in general, and in particular to Write Once Read Many (WORM) storage devices. Still more particularly, the present invention relates to a method and apparatus for selectively erasing data from a WORM storage device.
2. Description of Related Art
Many commercial organizations are required to have data retention policies, and the length of a retention period depends on the type of data and the associated business. For example, equities trading companies are required to retain all traders' e-mails and instant messages for approximately five to seven years. In addition, the retention method must be of the Write Once Read Many (WORM) type, as commonly required by most governing bodies. With a WORM storage medium, a record cannot be modified or tampered with after the record was written. CD-ROM is one type of well-known WORM storage medium.
While it is required to retain certain data for the statutory period, it is also highly desirable to ensure that such data are destroyed after such period has been expired. Thus, at the expiration of a data retention period, the conventional practice is to physically destroy the WORM storage medium because the continued retention of the data would represent a potential liability otherwise.
The conventional practice would not pose any problem if the retention period of all data on a WORM storage medium expired at the same time because the entire WORM storage medium could simply be destroyed. However, with a typical storage medium, such as a tape cartridge, it is most likely that some files recorded on the WORM storage medium may have passed their expiration date while others may not have. In addition, if there is an ongoing investigation, some records are required to be retained for a longer period. Such situation of having records that needed to be obliterated and records that needed to be retained on the same WORM storage medium is very undesirable. The nature of a WORM storage medium being that it is “tamper proof,” it is not acceptable simply to copy the data that needed to be retained onto another storage medium because the original certifiable record must be retained also.
One possible solution for alleviating the above-mentioned problem would be to store fewer records on each WORM storage medium in order to limit the exposure of collocated data artificially extending the life of expired data. However, such solution is undesirable in terms of cost and storage space, not to mentioned it runs counter to the continuing trend of larger and larger storage capacities in a single WORM storage medium.
Consequently, it would be desirable to provide an improved method for selectively erasing data from a WORM storage medium.